During the manufacture of refiner-mechanical or thermo-mechanical fiber pulps, the lignocellulose-containing materials being processed in the refiner are supplied with a considerable amount of energy, and the moisture which follows along with that material is repidly vaporized, since a temperature above 100.degree. C. is usually generated by the friction therein. Thus, valuable heat leaves the process and in fact has to be conducted away from it, since if this is not done disturbances in the material flow between the refining discs will generally occur.
During separation of these vapors one of the difficulties encountered is that the processed material is usually discharged to an apparatus which operates at a pressure which is considerably lower than the pressure prevailing in the refiner. Thus, vapors can follow along with this material and be lost. An additional problem is to insure that vapors are efficiently separated so that the fiber content remaining therein is relatively low. If this is not done, fibers following along with the vapor may precipitate out on the surfaces of the heat exchanger, for example, and thereby deteriorate the heat transfer obtained therein.
In the past attempts have been made to eliminate these problems by blowing the vapor and the fibrous material to a pressure-proof cyclone. In such a cyclone, the fibrous material is separated in a known manner and discharged by a thick-pulp pump, a cell outfeeder or the like, through the lower portion of the cyclone, while the vapors leave through the top of the cyclone. This system, however, involves shortcomings in that a large portion of the vapors are consumed in transporting the material to the cyclone, and in the cyclone operation itself, and furthermore because the investment and operation costs are rather high. As an example, it can be noted that at an overpressure of 1.5 kp/cm.sup.2 in the refiner the vapors obtained from the cyclone normally have an overpressure of only 0.75 kp/cm.sup.2. There is, consequently, a substantial reduction in the heat content thereof.
Such a system is shown, for example, in FIG. 1 of Finnish patent specification 58171, and in that inventor's improvement shown in FIG. 2 thereof. In particular, in that case there is a pressure-tight connection between the refiner housing and a discharge screw 5 leading from that refiner to a conveyor for removing the cellulosic material in the form of a plug and an outlet 12 including a screw 14 for separating additional cellulosic material from the vapor.
In accordance with the present invention, however, it has been surprisingly discovered that the use of such cyclones can now be entirely replaced by a system which includes an outfeed or discharge chamber in which the fibers settle.
The characterizing features of the present invention will be more fully understood with respect to the following detailed disclosure.